Laboratory instruments of this kind serve for example as analytical balances in many fields of industry, particularly in laboratories of research- and development departments, and also in production facilities, for example in quality control.
An analytical balance with a working compartment is described in detail in U.S. Pat. No. 4,700,793 A, which is commonly-owned, although now expired. Analytical balances are balances with a high resolution of the weighing result. Consequently, even the smallest extraneous influences affecting the weighing object or the load receiver can cause an error in the weighing result. The extraneous influence factors are rarely stable, and this can lead to situations where the exact weight of the weighing object cannot be determined. To protect the weighing system from being influenced by the ambient environment, a working compartment is therefore enclosed with a so-called draft shield.
As described in U.S. Pat. No. 4,700,793 A, the draft shield of an analytical balance has in most cases two slidable sidewalls and possibly also a slidable top cover, as the delivery of the weighing material to the load receiver usually occurs from the side, in some cases also from above. Normally, the front wall is rigidly connected to the housing of the balance, acting as a supporting element and thereby lending stability to the draft shield. Whenever possible, “slicing” closure means are preferred, meaning that for example slidable sidewalls are preferred over swiveling sidewalls. The closure means in the present context are referred to as “slicing” if in their opening and closing movements they slice the air and thus cause only a very small amount of air movement. This helps that the air inside the working compartment comes to rest very quickly. In addition, the air in the working compartment is shifted around only to a minimal extent, so that the temperature inside the weighing compartment can settle into a relatively stable profile over the height of the weighing compartment. In comparison, closure means that swivel will set large air masses into motion inside the weighing compartment. For a short time during opening and closing, a pressure difference occurs between the working compartment and the ambient space, with the pressure then equalizing itself through leaks in the draft shield, whereby air movements are caused again inside the working compartment.
A draft shield further needs to be of a stable design to hold its shape, so that harmful air movements of the ambient environment will not deform the walls and no air movements which could occur as a result of such deformations will propagate into the working compartment.
To facilitate the cleaning of the working compartment and in particular the sidewalls, a draft shield is proposed in commonly-owned U.S. Pat. No. 6,686,545 B2, whose front wall and sidewalls can be released from a form-fitting attachment by means of a swivel movement and can be removed from the balance through a subsequent pulling movement. The top cover is connected by a linear sliding guide to the balance housing which serves as rear wall and can be pushed back horizontally over the balance housing, whereby the draft shield is set open in the upward direction. Furthermore, the top cover can also be separated from the linear sliding guide by means of a swiveling movement.
With the trend to introduce time-optimized work processes, one finds more and more applications where different operations are performed, either simultaneously or following each other, directly in the working compartment without repeatedly putting the weighing object on and off the load receiver. This applies in particular to the preparation of solutions or powder mixtures. The design of a multi-functional working compartment is disclosed for example in commonly-owned U.S. Pat. No. 6,603,081 B2. This reference demonstrates how a multitude of devices such as for example dosage-dispensing units, holder devices for source containers and receiving containers, protective shield panels, indicator displays and the like can be installed on a temporary basis in the working compartment in a way that is optimized for a specific work process. As a result, an analytical balance which was originally designed only for weighing becomes a multi-functional laboratory instrument.
The draft shield devices of the known state of the art are optimized primarily for putting a weighing object on the load receiver and/or removing the weighing object after the weighing. These movements normally occur from the side, so that a serial weighing process involving a plurality of weighing objects can be performed in an optimal way for example if the objects to be weighed are delivered to the load receiver from the left side and, after the weighing, are taken off the load receiver from the right side. Furthermore, the weighing materials can also be delivered to the load receiver from above if the top cover is slidable.
However, the broadening of the functionality of the laboratory instruments described above makes it necessary to provide better access to the working compartment. It is therefore the object to propose a working compartment which is improved in regard to its accessibility during the work process.